merican elections are peculiar instruments of democracy, because they are so consistent in whom they leave out. In the past three Presidential elections, about forty-five per cent of those eligible to vote chose not to. And although this fact has been the subject of some public-spirited anxiety, it has generally not troubled political scientists too much, because it seemed as if non-voters had more or less the same view of the parties as voters did. Stretch the electorate to two-thirds of those eligible, or three-quarters, or make voting mandatory, and it has long seemed that the votes would be distributed in roughly equivalent proportions: about half the vote for Democrats, half for Republicans, with some variability reserved for the shape of current events.

But compare voters to non-voters and you get two very different-looking groups. The non-voters are younger, according to a 2014 Pew study. They are also less educated and have lower incomes. On the whole, there are fewer Protestants and more Catholics among non-voters than among voters, as well as fewer whites. Non-voters and voters might have roughly the same view of the Democrats, but you wouldn’t expect them to have the same view of much else.

In 2013, the political scientists Jan Leighley, of American University, and Jonathan Nagler, of New York University, published the results of a study that compared, among other things, the political views of voters and non-voters, dating back to 1972. On most social issues (abortion, L.G.B.T. rights), there was no measurable difference between them. Non-voters were more inclined toward isolationism. (Leighley and Nagler thought this might be because non-voters knew more soldiers than voters, and were more reluctant to see them sent into conflict.) The difference on economic matters was much more dramatic. Non-voters, Leighley and Nagler found, favored much more progressive economic policies than voters did. They preferred higher taxes, and more spending on schools and health care, by margins that hovered around fifteen per cent. “The voters may be representative of the electorate on some issues,” Leighley and Nagler wrote, “but they are not representative of the electorate on issues that go to the core of the role of government in modern democracies.” That non-voters had the same partisan preferences as voters only seemed to strengthen the finding—they wanted more redistribution regardless of whether they were Democrats or Republicans.

As unpredictable as this Presidential campaign has been, its two most successful outsider candidates, Donald Trump and Bernie Sanders, have in this sense followed established patterns: they have run campaigns that seemed perfectly matched to the preferences of people who do not normally vote. Both Sanders and Trump have done little to distinguish themselves from their parties on social issues, but they have moved to their parties’ left on economic matters and suggested that they would be more skeptical of international entanglements. If you were targeting non-voters on the right, you would design a campaign that looked very much like Donald Trump’s. If you were targeting non-voters on the left, you would emphasize almost exactly the same issues as Bernie Sanders.